The invention relates generally to monitoring systems for double pneumatic safety valves of the type used to control pneumatically-actuated clutches and/or brakes for presses or other such pneumatically-actuated devices.
In order to provide improved safety for pneumatically-actuated tools, such as stamping presses or the like, double safety valve assemblies have been provided between the pressurized air inlet and the supply to the pneumatically-operated device. In such arrangements, pressurized supply air cannot be supplied to the pneumatically-operated device from the pressurized air inlet unless both of the valve elements in the double safety valve are in an open position. The intent of such arrangements is that a malfunction of one of the valve elements will prevent continued actuation of the pneumatically-operated device.
However, because of various factors or features frequently found in such arrangements, it is sometimes possible for the pneumatically-actuated device to be partially operated even when one of the valve elements is stuck in an incorrect position or otherwise faulted. Whether such an undesirable malfunction can occur depends to some extent on whether the faulted valve is stuck in its closed position or in its open position. If if in its closed (or exhaust) position, it is less likely for the remaining valve to be capable of continuing to operate or actuate the system. If the stuck valve is in its open position, however, depending on the configuration of the system involved, it is sometimes possible to continue to at least partially operate the device with the remaining operable valve. In such an instance, the operator may not be aware of the malfunction or faulted condition of one of the valve elements unless an adequate monitoring system is present In other situations, even though normal operation cannot be continued in the event of one of the valve elements being in a stuck or otherwise faulted position, the pneumatically-actuated device may unexpectedly and undesirably partially actuate from a safe condition to an unsafe condition. Since this type of malfunction can occur with no warning, serious injury to personnel or property can result.
Thus, it has become advantageous and important to provide some form of monitoring system that will indicate to the operator that one or both of the valve elements is stuck or otherwise in a faulted condition. Various examples of double safety valve arrangements, with and without monitoring systems, can be found in the prior art, with such examples including the disclosures of U.S. Pat. Nos. 2,906.246; 3,757,818; 3,858,606; RE 28,250; 4,181,148; 4,257,255; 4,345,620; and 4,542,767. The disclosures of these references are thus hereby incorporated by reference herein for purposes of providing a background for the present invention.
In addition to the above, in pneumatic systems involving double safety valves of the type discussed herein, some monitoring systems include a feature that is intended to cause a safe shutdown of the pneumatic system for purposes of preventing undesirable or unsafe continued operation or partial actuation of the pneumatically-operated device. However, some of such monitoring systems have not adequately provided for such a safe shutdown of the system in all instances. Examples of such monitoring systems include those that are incapable of detecting a sticking or sluggish valve element, incapable of detecting whole or partial malfunctions of the monitoring system itself, or incapable of adequately safeguarding against actuation of the pneumatically-operated device when a reset function is operated without the malfunction of the double safety valve or the monitoring system being first properly corrected.
Thus, the need has arisen for a double safety valve system that provides adequate monitoring functions to inhibit further operation of the pneumatically-actuated device in the event that either of the valve elements in the double safety valve is out of sequence with the other valve element. In addition, it is an objective of the present invention to provide adequate safeguards inhibiting further operation in the event of a sticking or unacceptably sluggish monitoring valve element or other malfunction of the monitoring system itself. Thus, the present invention seeks to provide a double safety valve monitoring arrangement for pneumatic systems that is self-monitoring, both with respect to the double safety valves and with respect to the monitoring system itself.
The present invention also seeks to provide a monitoring system that is constantly dynamic during operation of the system in order to substantially reduce the possibility of a faulted, sticking, or sluggish valve element in the monitoring system itself. Still another objective of the present invention is to provide such a monitoring system wherein the amount of sluggishness or delay in valve element movement that will be tolerated before causing a shutdown of the system can be preselectively chosen or altered in order to suit the design parameters of a given installation.
Additional objectives, advantages, and features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.